Gears for speed changing, namely devices used to vary the speed of transmission between a drive shaft and a driven shaft, are well known.
Speed variation may be made by mating cog wheels fitted with differing numbers of cogs, or by friction systems such as moving transmission belts over bevel gears.
In the first case a high level of efficiency, and high degree of precision are obtained as only rolling friction is determined, but variation is uneven and needs compensating devices such as the clutch in automobile vehicles.
In the second case, as a consequence of the sliding friction necessary between driving and driven parts, much efficiency is lost, parts wear out quickly and operation is irregular.
Specifically in the field of cycles and motorcycles, speed change is made by moving the transmission chain over from one cog wheel to another, using devices which are both complex and delicate.
The types of speed change devices with gears inside the hub have complex structures and are therefore both bulky and costly.